The indictment prepared by Special Counsel Robert Mueller charged all with conspiracy to defraud the United States by seeking to undermine the Federal Election Commission, the Department of Justice and the Department of State.

It "serves as a reminder that people are not always who they appear to be on the Internet”, said Deputy Attorney General Rod Rosenstein in announcing the indictment.

"The indictment alleges that the Russian conspirators want to promote discord in the United States and undermine public confidence in democracy. We must not allow them to succeed," he said during a brief appearance before the media.

In addition to charging the 16 defendants with conspiracy to defraud the U.S., the Internet Research Agency (IRA), a Russian company based in St. Petersburg, Russia, and two individuals are charged with conspiracy to commit wire fraud and bank fraud.

Four defendants and the agency are also charged with aggravated identity theft.

The IRA was primarily funded by Viktorovich Prigozhin, a Russian businessman close to President Vladimir Putin, and his companies Concord Management and Consulting LLC, Concord Catering and other subsidiaries, according to the indictment.

The court documents suggest the IRA was part of a larger Prigozhin-funded operation called Project Lakhta.

The IRA's efforts to interfere with the U.S. political process, including the 2016 race for the White House, began as early as 2014. It included creating hundreds of social media accounts of fake U.S. personas that stoked political discord by supporting "radical groups".

It also bought political advertisements on social media web sites to promote their social media groups with payments worth thousands of dollars each month, according to the documents.

With the election nearing, the IRA turned its efforts to denigrating failed Democratic candidate Hillary Clinton and boosting support for then-Republican candidate Donald Trump starting in early to mid-2016.

After U.S. social media companies disclosed they were working with the investigation into Russian interference, one of the defendants, Irina Viktorovna Kaverzina, allegedly sent an email to a family member saying: "We had a slight crisis here at work: the FBI busted our activity (not a joke). So I got preoccupied with covering tracks together with the colleagues."

"I created all these pictures and posts, and the Americans believed it was written by their people," she allegedly added.

President Donald Trump cited the indictment as vindication of his claims that neither he nor his campaign colluded with the Russian effort.

"Russia started their anti-US campaign in 2014, long before I announced that I would run for President. The results of the election were not impacted. The Trump campaign did nothing wrong - no collusion!" Trump said on Twitter.

Mueller's probe is ongoing and could result in further charges, however, and the question of the Trump campaign's possible collusion has been at the center of the investigation.